1. Field of the Invention
The present invention relates to a finishing throwaway ball endmill used widely in machining of dies and in copying and profiling, and more particularly, to a finishing throwaway ball endmill which has a blade tip adapted to make a firm attachment to a body thereof with easy.
2. Discussion of the Related Art
In general, the throwaway ball endmill has a steel body and a cemented or sintered carbide blade tip screwed firmly on the body.
FIGS. 1.about.3 respectively illustrate a perspective disassembled view, and an assembled plane and a front views of an exemplary conventional finishing throwaway ball endmill.
This kind of conventional finishing throwaway ball endmill has two blade tips 2 and 3 of shapes different from each other screwed on both sides of the body 1 by screws 4. However, in this kind of throwaway ball endmill, each of the blade tips can not be securely fixed to the body 1 because it is fixed by only one screw, and the precision of the endmill is low because two different blade tips are fixed on the same body. And, as shown in FIG. 2, the removal of substantial portion of the body 1 for attachment of the blade tips 2 and 3 to form tip attaching parts 1a causes the body 1 weakened to generate vibration on the throwaway ball endmill, which subsequently causes breakage of the tips 2 or the screws loosened.
FIGS. 4 and 5 respectively illustrate a perspective disassembled view, and an assembled front view of another exemplary conventional finish throwaway ball endmill using two screws for fixing an unitary blade tip.
This kind of conventional throwaway ball endmill has, as shown in FIG. 4, a slot 11c formed in a body 11 from an end thereof to a certain depth along an axis of the body 11, and a blade tip 13 inserted in the slot 11c and fixed to the body 11 by two screws 15a and 15b of different shapes. In detail, the blade tip 13 has two screw pass-through holes 14a and 14b formed along the axis of the blade tip 13 and a V wedge 13a formed at a fore end thereof inserted in the slot 11c. The body 11 has screw pass-through holes 14a and 14b for the blade tip, screw inserting holes 12a and 12b formed opposite to the screw pass-through holes 14a and 14b, and a V bottom 11a formed to be matched to the V wedge 13a. Particularly, of the screws 15a and 15b, the screw 15a has a neck part (part without thread) 15c machined such that it can be precisely fitted to the screw pass-through hole 14a when the V wedge 13 on the blade tip 13 is closely fitted to the V bottom 11a in the body 11. Accordingly, when the blade tip 13 is inserted in the slot 11c in the body 11 and the two screws 15a and 15b are inserted into the screw inserting holes 14a and 14b and the screw inserting holes 12a and 12b and fastened, the blade tip 13 is fixed to the body 11. However, when the V bottom 11 in the body 11 is weared down from prolonged use, causing the V wedge 13a on the blade tip 13 can not make close contact with the V bottom in the body 11, the mounting of the blade tip 13 became unstable, thereby causing problems that the precision of the ball endmill is degraded and the rigidity of the body 11 is degraded due to stress concentration occurred at the ends of the V bottom 11a.
And, the machining of the two screw inserting holes 14a and 14b in the cemented or sintered carbide blade tip 13 causes the productivity low, and the attachment of the blade tip 13 with the two different screws 15a and 15b delays assembly of the ball endmill.